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Process considerations Threading methods

Existing – Is the process stable today – Is the productivity maximized – Is chip control acceptable – Is the quality of the thread

acceptable

New Is the component

• symetric/ asymetric • stable/vibration sensitive

What are the requirements • Finish • Tolerances

–Will I have clearance behind the thread or is it against a shoulder/blind hole

–Is this material easy or difficult from a chip control point of view

–Is the material work hardening

Always ask: “Should this component be thread turned or thread milled”

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Basics in threads Our standard profiles

Application Insert Thread form Thread type Code

General threads ISO metric American UN

MM UN

Pipe threads Whitworth NPT British Standard (BSPT) NPTF American National Pipe Threads

WH, NT PT, NF

Food and fire Round DIN 405 RN

Aerospace MJ UNJ

MJ NJ

Oil and gas

API Rounded API ”V” form 60°

RD V38, 40, 50

API Buttress VAM BU

Motion threads Trapezoidal/DIN 103 ACME Stub ACME

TR AC SA

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Insert types V - profile

Advantages – Flexibility – one insert can be used for

several pitches. – Reduce or eliminate vibrations due to

reduction in cutting pressure – Minimum tool inventory

Disadvantages

– Needs a preform diameter – Burr formation – The nose radii is designed to offer the

smallest pitch, which reduces tool life

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Insert types Full profile

Advantages Forms a complete thread profile, including the

correct depth, bottom and top radii for a strong thread

High productivity due to elimination of subsequent operations.

In general this insert makes a cleaner thread which requires less deburring

Disadvantages

– Different inserts for every pitch and profile – As the insert is generating both the root and crest,

the tool pressure can increase, putting more requirements on the setup

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Insert types Use extra stock/material for topping the thread

When a full profile insert is used the blank should not be turned to exact diameter prior to the threading

Add extra stock/material on the workpiece for topping the finish diameter of the thread

Extra stock/material should be 0.03-0.07 mm (.001-.003 inch)

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Infeed Three different types of infeed

The infeed method can have a significant impact on the thread machining process. It influences – Chip Control – Insert Wear – Thread Quality – Tool Life

In practice, the machine tool, insert geometry, workpiece material and thread pitch influence the choice of infeed method

Radial infeed

Alternating infeed

Modified Flank infeed

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Infeed Modified flank infeed

Chip is similar to that in conventional turning - easier to form and guide

Chip is thicker, but has contact with only one side of the insert

Insert wear dominant on one flank

Less heat is transferred to the insert

First choice for most threading operations

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Modified flank infeed

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Infeed Opposite flank infeed

Insert can cut using both flanks – the chip can be steered in both directions

Better chip control

Helps to ensure continuous, trouble-free machining, free from unplanned stoppages

Chip flow

Feed direction

Chip flow

Standard modified flank infeed

Opposite flank infeed

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Infeed Radial infeed

Most commonly used method Makes a stiff “V” chip Even insert wear Insert tip exposed to high temperatures,

which restricts depth of infeed Suitable for fine pitches Vibration possible and poor chip control

in coarse pitches

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Radial Infeed

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Application Alternating infeed

First choice for larger thread profiles

Recommended for pitches larger than 5 mm (5 t.p.i)

Special CNC machine program is required

Chips are directed both ways, making control difficult

Even insert wear and longest tool life in very coarse threads

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Alternating flank infeed

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Infeed Application Decreasing depth per pass (constant chip area)

First choice in all threading operations

Most commonly used method to improve the machining result

The first pass is the deepest

Follows recommendation on infeed tables in catalog/calculator

More “balanced” chip area

Even load on insert

Last pass around 0.07 mm (.003 inch)

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Infeed Application Constant depth per pass

Each pass is of equal depth, regardless of number of passes

More demanding on the insert

Can offer better chip control

Increases the required number of passes

Should not be used for pitches larger than 1.5 mm or 16 t.p.i.

A less-productive method

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Three different geometries

F-geometry Sharp geometry

C-geometry Chip breaking geometry

All-around geometry First choice in most operations

C-Geometry For best chip control use with

modified flank infeed of about 1o

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Geometry Radial infeed C - Chip breaking geometry

Insert: 266RG-16UN01C180M 1125 Pitch: 18 t.p.i. Vc: 500 sfm NAP: 6 Infeed: Radial

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Geometry Modified flank C - Chip breaking geometry

Insert: 266RG-16UN01C180M 1125 Pitch: 18 t.p.i. Vc: 500 sfm NAP: 6 Infeed: Modified flank

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